[DCoder]

Isolation and reproduction.

For one thing, you want the development environment to be as similar to production as possible – same OS version, same webserver version, same DB version, same dependencies, no unwanted extras that differ between environments.

For another thing, you don't want to have to solve conflicts between project A and completely unrelated project T if you need to work on them both.

[tvon]

If you care about isolation and reproduction then you're using a VM anyway and the host OS is completely irrelevant.

[DCoder]

Using a VM is the reason to use Vagrant.

[tvon]

Yes, I know.